1. Field of the Invention
The invention relates to a cleaning system for washing cylindrical surfaces of rotating bodies of a rotary printing press, such as printing-forme and rubber-blanket cylinders, impression cylinders, damping-solution or inking-unit rolls. The invention also relates to a method of controlling the introduction of cleaning fluid for a cleaning system for rotating bodies of a rotary printing press.
2. Description of the Related Art
During the printing of each edition, more or less severely disruptive dust, coating or fibrous constituents from the paper are, for example, deposited on the rubber blanket in the printing unit of a rotary press, or, together with paper fillers or loose paper fibers, the printing ink forms a layer, which have a considerable influence on the print quality resulting from such more or less severe build-up phenomena.
In the press, therefore, considerable quantities of organic solvents are still used, in particular for cleaning fluids. Quite specific hazards originate from the solvents, depending on the type of solvent, such as the risk of fire and explosion, but also risks to the health of the print shop staff.
At present there are two approaches to neutralizing the health hazards to the print shop staff. Firstly, the use of automatic cleaning systems and a detergent recycling system is normal nowadays. As a result of the use of automatic cleaning systems, the consumption of cleaning agent can be reduced considerably. Secondly, the replacement of the organic solvents by cleaning agents on a vegetable basis is intended. Cleaning agents made from vegetable oil do not meet all the desired requirements in an optimum way, at least at present.
The automatic cleaning system used nowadays comprises brush systems, washing-cloth systems, in particular towelling systems, and spraying systems. In the case of the towelling system, as a rule the towelling roll is cleaned by a doctor and wetted with clean detergent. In the washing-cloth and brush system, as is known the cleaning element is pressed against the cylinder or roll surface to be cleaned. In the washing-cloth system, during the washing period, the cloth is wound repeatedly onward from a clean-cloth roller to a dirty-cloth roller. The washing cloth or the brush and/or the cylinder surface are wetted with cleaning agent via a nozzle spraying device. In a spraying system, solvent and/or water is sprayed, for example, onto the rubber blanket or onto the cylinder surface to be washed. Printing ink and existing paper constituents begin to be separated and are then either doctored off or picked up by the washing device, for example by the washing cloth or the towelling roll, or picked up by the moving paper web. The small cross section of an automatic cleaning system on the spraying system, having a washing bar which is installed, for example, on the paper inlet side (but other positionings are also conceivable) permits installation even in the event of difficult space conditions.
As already outlined at the beginning, automatic cleaning systems in presses therefore use, as cleaning agents, fluids from which during operation, but in particular in the case of a fault in the cleaning system, a hazard to humans and system can originate. The main hazard in this case originates from the flammable cleaning agent which is used, which can come into contact with hot surfaces (for example in the dryer in the case of heatset inks). According to the prior art, therefore, the quantity of fluid per unit time is limited (below a determined critical quantity) in such a way that ignition of the mixture which forms after the liquid cleaning agent has changed to the gaseous state cannot take place.
In order to increase the machine safety of the cleaning system, the intention in addition is to prevent unintended emergence even of small quantities of the cleaning agent per unit time, that is to say the adjustment of the system is to be carried out in an optimum way with regard to the necessary quantity of cleaning agent, which is characterized by the actual spraying time. Here, it is not possible to make any concrete statements, since each machine and each system is different. In addition, the papers and cleaning agents used, including the solvents, have an influence on the washing operation. For this reason, as a rule appropriate trials have to be carried out in order to achieve the optimum results.
Because of the risk of ignition of the cleaning agent which, for example, can be given by transporting a supercritical quantity into the dryer of the press by means of the paper web, it must be possible to meter the feed of cleaning agent very accurately.
This requirement is currently met by so-called metering pumps, which are controlled from an operating panel. A critical precondition for the necessary success is therefore the correct adjustment of the system with regard to the requisite quantity of cleaning agent, which is characterized by the actual spraying time. The quantity of cleaning agent per unit time which is introduced into the press is therefore restricted below the respective critical value which is permitted for the dryer of the press with respect to the ignition capability of the cleaning agent. The parameters to be taken into account in this case are the composition of the cleaning agent and the dryer characteristics.
For example, EP 0 570 727 A1 describes a cleaning system for a rotary press which is constructed in such a way that it operates under automatic control, and the fluid expulsion quantities and fluid expulsion times of the spraying units can be adjusted individually and controlled automatically. In this case, the cleaning agent can in each case be sprayed by means of a nozzle bar directly onto the rotating press parts or onto a cleaning element such as a washing cloth, for example (see DE 100 08 214 A1) or brush roll. The nozzle bar or bars are connected via an intermediate reservoir and non-return valves, which open in a direction to the intermediate reservoir and close in the opposite direction, to fluid feed lines to which the cleaning agent can be fed in a precisely metered manner by a metering pump. The metering pumps are actuated by controlled valves. The metered quantity of fluid put into the intermediate reservoir in each case is then expelled through the nozzle bar by a compressed-air column and sprayed out. This cleaning system is suitable for the wet cleaning of rotating press parts such as blanket cylinder, conventional or digitally imaged (CTP) forme cylinder, impression cylinder, ink transfer rolls and so on of presses.
However, the use of metering pumps with regard to their ability to be placed locally in the system and the overall size, and also the necessity to use fluid feed lines of equal lengths, and the necessity for additional devices such as non-return valves, entails disadvantages caused by the principle. If it is wished to avoid fluid lines of unequal length or excessive length to supply a plurality of nozzle bars, then a separate metering pump will be needed for each nozzle bar and each type of fluid, so that for example in the case of two nozzle bars which each have to be supplied with two different fluids, four metering pumps are required. As a rule, metering pumps constitute costly special fabrications which occur in many variants in the whole of automation technology. Furthermore, complicated calibration activity is required. In particular, in the case of central supply, only individual calibrations are possible and many individual lines are required. A system incorporating metering pumps is certainly entirely robust with respect to a series of fault influences, but permits no conclusions about the serviceability of the plant.
On this basis, the invention is based on the object of developing an automatically controlled cleaning system of the type outlined at the beginning in such a way that its serviceability can be monitored, in particular erroneously exceeding the critical quantity of cleaning agent per unit time during the cleaning of the rotating elements of the press (leakage) can be detected and countermeasures can be initiated. Furthermore, this object is to be achieved with means which are simple in design terms and, as compared with metering pumps, are more cost-effective and give rise to no concern with respect to the risk of fire and explosion.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.